Adhesion of tumor cells to endothelial cells is a crucial step in the complex sequence of metastasis. In addition to type and local density of adhesion molecules on both cell types, shear forces exerted by the blood flow have been described to be of major importance in governing cell adhesion. Most of the experiments on the molecular basis of tumor-endothelial cell adhesion have been performed as static assays which lack shear forces. We have developed an artificial venule which shares the following in vivo characteristics. A confluent layer of endothelial cells lines the luminal surface of a glass capillary of 1 mm i.d. with pores of 30 nm diameter to allow diffusion of molecules from outside the capillary. Physiological pressure of 16 mbar, flow rate of 2 cm/s, and shear forces of 2 dynes/cm2 are maintained. This device allowed us to show that under dynamic conditions adhesion of B16 mouse melanoma cells to EA.hy926 endothelial cells is mediated most likely by a lectin-like structure on B16 cells and oligosaccharide(s) on endothelial cells. In addition, endothelial activation-independent adhesion was found to be restricted to only a fraction of endothelial cells, as the number of B16 cells that adhered was independent of the number of B16 cells applied.